Field of the Invention
The present invention relates to power semiconductor components, compensation components, power transistors, and methods for producing power semiconductor components. The power semiconductor component has a drift path of a first conduction type disposed between two electrodes and to a method of producing these power semiconductor components.
Power transistors, such as DMOS transistors, UMOS or trench transistors, and similar semiconductor elements necessarily contain in their structure a xe2x80x9creverse diodexe2x80x9d composed of a body region (also called a channel region) and a drain region. In numerous applications, this reverse diode is regularly operated in the flow direction, for example, as a freewheeling diode.
In the case of a reverse diode operated in the flow direction, a current flows through the MOS transistor in the reverse direction. This current in the reverse direction is not a channel current but a diode current associated with a high flood of charge carriers.
If the power transistor previously operated in the reverse or blocking direction is then switched over to the forward direction, then it absorbs voltage in the forward direction. For this purpose, the charge carriers specifically stored in the drift path of the power transistor have to be extracted from the semiconductor body of the power transistor. This process entails a high reverse diode current. Here, the reverse diode current adds to the load current of the power transistor and, in this application, leads to increased switching losses, for example in a second transistor which has to carry the entire current when it is turned on.
In compensation components like those described in U.S. Pat. No. 4,754,310 issued to Coe, the peak value of the reverse current (i.e., xe2x80x9cthe reverse current peakxe2x80x9d) is very high. A high reverse current peak is already accompanied by problems. In addition, the reverse current in compensation components returns to zero very suddenly and xe2x80x9cbreaks downxe2x80x9d. Break down necessarily includes stray inductances that can lead to dangerous overvoltage peaks.
Previously, in order to avoid the above difficulties, a Schottky diode has been connected in antiparallel with the power transistor. The Schottky diode has a lower threshold voltage than the pn-reverse diode of the power transistor. Accordingly, the Schottky diode can accept the reverse current if the Schottky diode has a sufficiently-small, overall forward voltage drop. However, this is barely possible, especially in the case of higher-value blocking semiconductor components, because the Schottky diode would require the same blocking ability as, for example, a power transistor.
A further, previously considered possibility for overcoming the above difficulties with power transistors is not to connect its body or channel region to the source contact. This allows the pn-junction between source region and body region to absorb the necessary reverse-blocking voltage.
In such a power transistor having a body region that is floating and not connected to the source contact is that, in the forward direction between collector and emitter with an open base, one disadvantage is preventing the breakdown of a parasitic npn-(or pnp-) transistor composed of the source region, the body region, and the drain region must be prevented. This is extremely difficult and complicated in technological terms. One possibility is to minimize the gain of this parasitic transistor with an inlaid recombination zone, for example, a floating metal or silicide contact. However, in such a case, the gain remains high in an interspace between such a recombination zone and the gate of the power transistor. For this reason, the interspace should be configured to be as small as possible, in order to prevent breakdown of the parasitic transistor (called the UCEO breakdown).
If the body region is not connected to the source contact, then it is not at a fixed potential. The turn-on voltage of the power transistor via the substrate control effect therefore depends on the drain-source voltage applied. In addition, a breakdown must be prevented between collector and emitter with open base of a parasitic npn-(or pnp-) transistor composed of the source region, the body region, and the drain region, which is difficult in technological terms.
U.S. Pat. No. 5,202,750 issued to Gough discloses an emitter switched thyristor, specifically an EST, as it is called, in which, an n-doped emitter region can be connected to the cathode or isolated from the latter via an MOS channel. This thyristor has on its rear, a p-doped region that acts as a p-doped emitter. This structure can switch off the thyristor, which has a very high conductivity as a result of charge carrier flooding with minority charge carriers and majority charge carriers, by driving the MOS channel via the associated gate.
It is accordingly an object of the invention to provide a power semiconductor component, a compensation component, a power transistor, and a method for producing power semiconductor components that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that specifically provide a reverse-blocking power semiconductor component that, in the reverse direction, has a blocking capacity of at least a few volts, so that in the presence of a voltage in the reverse direction, no reverse diode current flows through the semiconductor component. In addition, the method of producing such a reverse-blocking power semiconductor component is to be specified.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a reverse-blocking power semiconductor component. The reverse-blocking power component includes two electrodes, a drift path, a region, and a gate. The drift path of a first conduction type is disposed in an area between the two electrodes. The region is disposed in the drift path and subdividing the drift path into two areas. The region is of the other conduction type, opposed to the one conduction type. The gate is being provided with the region.
With the objects of the invention in view, there is also provided a method of producing the power semiconductor component. According to the method, the region that subdivides the drift path is produced by epitaxy.
The power semiconductor component according to the invention achieves its blocking capacity, which may be restricted to a few volts, in the reverse direction as a result of the fact that in the area of the drift path, an additional region doped opposite to the drift path is provided, so that the drift path is subdivided into two areas. If appropriate, more than just one such region may also be introduced into the drift path. The drift path is then accordingly subdivided into a plurality of areas. If, for example, two regions of the other conduction type, opposed to the conduction type of the drift path, are incorporated into the drift path, then there is a total of three areas, into which the drift path is subdivided.
In the following text, it will be assumed that the drift path is n-doped. In this case, the region inserted into the drift path is p-doped in order to subdivide it of course, however, the opposite conduction type may also be present in each case. This means that in this case a p-doped drift path is then subdivided into at least two areas by an n-doped region.
The p-doped (or n-doped) region inserted into the n-doped (or p-doped) drift path is not connected to the source contact or the body region. However, it divides the drift path into two completely mutually isolated areas, into n+1 areas in the case of n regions, so that at least one pn junction blocking in the reverse direction is produced between the p-doped region and the n-doped area on the source side of the drift path. In this case, in the case of a power transistor as a power semiconductor component, it is assumed that this drain is biased negatively with respect to its source.
Because this additional p-doped region also blocks the current flow in the forward direction in the case of a power transistor as a power semiconductor component, a second MOS gate disposed to produce an n-conducting channel, connecting the two areas of the drift path, in the inserted region. If there is a plurality of such regions, then the second MOS gate must be provided over these regions, so that all the areas of the n-doped drift path are connected by the n-conducting channel of this second MOS gate.
This second gate can be connected to the actual first gate, that is, the normal gate of the power transistor as an example of the power semiconductor component and in particular can be composed of its direct extension.
When the power semiconductor component is operated in the forward direction, the second gate is switched on together with the first gate. If the power semiconductor component is operated in the blocking direction (forward or backward), on the other hand, then both gates are switched off.
A substantial advantage of this reverse-blocking power semiconductor component according to the invention resides in the fact that its blocking capability in the forward direction remains unrestricted, and no collector-emitter breakdown of a parasitic npn-transistor composed of source, body, and drain occurs, and additionally that the body region remains at the fixed source potential, so that the turn-on voltage of the power semiconductor component does not depend, via the substrate control effect, on the drain-source voltage applied.
It is a second object of the present invention to provide a reverse-blocking power semiconductor component in which the body region is not connected, yet reliably prevents a UCEO breakdown of the parasitic transistor composed of source region, body region, and drain region is reliably prevented. In addition, the invention provides a method of producing a reverse-blocking power semiconductor component.
With the objects of the invention in view, there is also provided a reverse-blocking power semiconductor component including a semiconductor body, a body zone, a source metalization, and a body zone. The semiconductor body forms a drift path of one conduction type. The body zone of the other conduction type, opposed to the one conduction type, is provided in the semiconductor body. The source zone of the one conduction type placed in the body zone and connected to the source metalization. The region of the one conduction type is inlaid in the body zone to define a source-side part and a drain-side part in the body zone. The region inlaid in the body zone is short-circuited at least to the drain-side part of the body zone. The source metalization is connected electrically only to the source zone.
In the case of the power semiconductor component according to the invention of the second variant, the body region is not connected to the source metalization and is therefore floating. Therefore, it achieves a blocking capability in the reverse direction that may be restricted to a few volts.
However, in the forward direction, in the case of a floating body region, the breakdown voltage is reduced considerably with respect to a structure with a connected body region. The UCEO breakdown of the parasitic transistor composed of source region, body region, and drain region causes the reduction of the breakdown voltage.
The mechanism of the UCEO breakdown utilizes a blocking current produced in the spatial charging zone of the blocking pn junction between body region and drain region and enlarged as a result of avalanche generation or multiplication arrives in the body region as a hole current and therefore, as base current, drives the parasitic bipolar transistor. In turn, the parasitic bipolar transistor supplies an electron stream that is increased by the transistor gain of the parasitic transistor. In turn, the electron stream flows through the body region into the spatial charging zone, where avalanche generation restarts the multiplication process.
In order then to prevent the UCEO breakdown of the parasitic bipolar transistor composed of source region, body region, and drain region in the forward direction, the feedback mechanism for the multiplication process is interrupted in accordance with the invention.
In the following explanation, it will be assumed that the drift path of the power semiconductor component is n-doped, while the body region exhibits p-doping. Of course, however, converse conduction types are also possible.
In the body region, which in the present case is to be p-doped, an additional n-doped region (in the case of an n-doped body region, an additional p-doped region) is inlaid. The additional n-doped region is inlaid in such a way that electrons that come from the source region do not have a continuous path in the p-doped body region as far as the spatial charging zone of the blocking pn junction between body region and drain region. This additional region, n-doped in the present case, is connected electrically by a purely resistive or non-rectifying connection. Preferably, the connection includes, in particular, a metal contact, at least to the drain-side part of the body region subdivided by the additional region. In addition, a purely resistive connection can be disposed between the additional region and the source-side part of the body region.
Electrons that come from the source region, in the case of the power semiconductor component according to the invention, are intercepted by the additional region inlaid in the body region. Because the pn junction is definitely short-circuited, these electrons no longer can overcome the pn junction to the drain-side part of the body region as minority charge carriers.
In the case of the reverse-blocking power semiconductor component, the blocking capability in the forward direction is maintained unrestrictedly, because no UCEO breakdown occurs. Likewise, a UCEO breakdown can be prevented In the reverse direction. If the additional region inlaid in the body region is also short-circuited to the source-side part of the body region.
As previously discussed, the additional region is intended to be n-doped and is inlaid in the body region. The additional region functions as a collector of the respective parasitic bipolar transistor composed of source region, body region, and additional region in the case of blocking loading in the forward direction or, respectively, of drain region, body region, and additional region in the case of blocking loading in the reverse direction, and therefore collects electrons. Therefore, diffusion of the electrons toward the blocking pn junction between source region and body region is prevented.
As a result of the additional region inlaid in the body region, the feedback mechanism causing the UCEO breakdown as a result of multiplication in the spatial charging zone and the gain of the parasitic bipolar transistor is interrupted in a straightforward manner. The additional inlaid region intercepts the electrons emitted from the source region accomplishes this.
The invention includes a mode of operation of the reverse-blocking power transistor. An example of the reverse-blocking power transistor may be represented as a body region that is p-doped and the inlaid region that has the n-doping. The parasitic npn bipolar transistor composed of source region, body region, and drain region is subdivided into two series-connected npn transistors by the additional n-doped region inlaid in the body region. Of these two npn transistors, the first transistor, composed of the inlaid n-doped region, the body region, and the drain region, is operated with emitter-base short circuit, so that this first transistor has its full blocking capability. On the other hand, the other, second transistor composed of source region, body region, and inlaid n-doped region is brought into UCEO operation. Or, if the additional, inlaid n-doped region is also short-circuited to the source-side part of the body region, the second transistor is operated as a diode in the forward direction. Therefore, the second transistor has only a low or even no blocking capability; however, it does not need any such capability.
The power semiconductor component has a blocking capability of at least a few volts in the reverse direction, so that under a reverse voltage, no diode current flows through the power semiconductor component. In this case, the current can flow readily through an antiparallel-connected pn diode or Schottky diode with appropriate characteristics.
The power semiconductor component according to the invention, depending on the thickness and doping of the drift path, can block in the forward direction approximately between 30 and 1000 V. The drift path can then have doping between about 2xc2x71016 charge carriers/cm3 and 1xc2x71014 charge carriers/cm3, and can have a thickness of about 2 xcexcm to 100 xcexcm.
The power semiconductor component according to the invention is preferably a power transistor. However, the invention can also be applied in the same way to other power semiconductor components, such as IGBTs (bipolar transistors with isolated gate) and thyristors.
The semiconductor body of the power semiconductor component according to the invention is preferably composed of silicon. Instead of silicon, other suitable semiconductor materials, such as SiC, AIIIBv and so on can also be used.
A preferred area of application for the present invention is compensation components, in which compensation regions of the conduction type opposed to the conduction type of the drift path are inlaid in the latter. The compensation regions can be floating or connected to the body region.
The additional region inlaid in the body region can also be referred to as an xe2x80x9celectron collectorxe2x80x9d. This electron collector is short-circuited at least to the drain-side part of the body zone and preferably to the source-side part of the latter, which can be done through a metallic short-circuit by a metal contact or plug.
It is not necessary for there to be semiconductor material, in particular silicon, above the metallic short circuit or metal plug between the body region and the inlaid, additional region. It is also not important precisely where the metallic short circuit or metal plug is disposed. The metallic short circuit or metal plug also can be provided on the surface of the semiconductor body.
While, in the first variant of the power semiconductor component according to the invention, the drift path is xe2x80x9csubdividedxe2x80x9d, in the case of the second variant there is a xe2x80x9csubdivisionxe2x80x9d of the body zone. The drift zone and body zone also can be subdivided in each case to create a third variant.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a power semiconductor component, a compensation component, a power transistor, and a method for producing power semiconductor components, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.